If you really feel a need to stretch prior to tennis, do so before you get to the courts. Considerable evidence in the past 2 decades indicates that static stretches will reduce muscle performance (both speed & strength) for about 1 hour (possibly longer with extensive stretching and perhaps only 30 minutes or so for light stretching). There is no evidence that static stretches immediately prior to sports/exercise will prevent injuries. In some instances, extensive static stretches just prior to exercise/competition may actually increase the likelihood of injury.
Once you get to the courts, warmup up. It is not a bad idea to include dynamic stretches as part of your warmup. Do some sort of leg swinging to dynamically stretch the groin. After tennis or exercise, perform some static stretches as part of your cool down.
Every tool is a weapon -- if you hold it right. (~Ani DiFranco)